This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-289396, filed on Sep. 22, 2000, and No. 2001-269231, filed on Sep. 5, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical device, a surface emitting type device and a method for manufacturing the same.
2. Related Background Art
In various kinds of optical devices having a light emitting function, a light detecting function, a light modulating function, and the like, a distributed Bragg reflector (herein after referred to as DBR) having a high reflectance is used. The DBR is a reflector in which two kinds of materials having different refractive indexes are alternately laminated to reflect light by the use of a difference in the refractive index. A surface emitting type laser will hereinafter be described as an example of an optical device using the DBR.
The surface emitting type laser is a surface emitting type device which emits laser beam in a direction perpendicular to a substrate. This device is easily integrated two-dimensionally and is expected to be applied to a parallel optical information processing, an optical interconnection, or a data storage field such as an optical disc. As the surface emitting type lasers have been developed a GaInAs/GaAs base surface emitting type laser having a wavelength of 0.98 xcexcm, a GaAlAs/GaAs base surface emitting type laser having a wavelength of 0.78 xcexcm to 0.85 xcexcm, a AlGaInP/GaAs base surface emitting type laser having a wavelength of 0.63 xcexcm to 0.67 xcexcm. These surface emitting type lasers generally include a cavity comprising a n-type clad layer, an active layer and a p-type clad layer. And the lasers generally include DBRs formed on the upper and lower sides of the cavity. In the surface emitting type laser, it is necessary to make the reflectance of the DBRS, disposed at the upper and lower sides of the active layer, 99% or more.
In recent years, attention has been paid to a nitride semiconductor base laser using a nitride semiconductor having a large band gap and having a short wavelength of about 0.4 xcexcm. Such a short wavelength laser has various advantages such as increasing the packing density of an optical disc such as a DVD. For this reason, this nitride semiconductor base laser receives attention as the light source of the next generation of a high-density optical disc system, or the like.
However, a surface emitting type laser has not been put into practical use in the nitride semiconductor base laser. For one thing, this is because it has been difficult to make a DBR having a high reflectance described above.
That is, in the case of a nitride gallium base laser, a combination of semiconductor materials usable for the DBR includes a combination of GaN and AlGaN and a combination of GaN and AlN. However, even in the case where the DBR is constituted by a combination of GaN (n=2.57) and AlN (n=2.15), in which a difference in refractive index n is large, it is necessary to grow a multilayer film of 20 layers or more, in a minimum, so as to produce a required high reflectance. Accordingly, in the surface emitting type laser, it is necessary to grow a multilayer film of 40 layers or more in total of the upper and lower DBRS. However, in the case of a laminated structure of GaN and AlN, there is a large difference in lattice constant and an Al crystal is hard, so cracks are apt to be produced. For this reason, when the multilayer film of 40 layers or more is formed, the occurrence of the cracks can not be avoided, and manufacturing yield remarkably decreases. Further, since the growth rate of the multilayer film of GaN and AlN is slow, the forming of the multilayer film of 40 layers or more presents a problem of remarkably reducing productivity. In this manner, if a reflector having a high reflectance is formed of the nitride semiconductor, the reflector becomes a laminated structure of many layers, which reduces the manufacturing yield and productivity. Further, in the case of this DBR, a high reflection band (wavelength width of stop band) is very narrow. So, in the case of this DBR, oscillation conditions can not be satisfied even if the thickness of each layer of the DBR, the thickness of the cavity or the composition of the active layer are shifted a little from the design values. Hence, in the case of this DBR, stable laser beam can not be produced. From these reasons, the surface emitting type nitride semiconductor laser has not been put into practical use.
The present invention is based on recognition of aforementioned problems. It is therefor an object of the invention to provide a DBR which has a high reflectance and has a wide wavelength width of a stop band and is easily manufactured, in order to provide an optical device and a surface emitting type device each having a high efficiency and being operated stably and being manufactured at high yield, and to provide a method for manufacturing the same.
According to embodiments of the present invention, there is provided an optical device comprising a reflector for reflecting light, said reflector including a laminated layers having a plurality of semiconductor layers with substantially the same interval gaps therbetween, each of said semiconductor layers having substantially the same thickness and being made of a first nitride semiconductor containing aluminum.
According to embodiments of invention, there is further provided an optical device comprising a reflector for reflecting light, said reflector including a laminated layers in which a plurality of semiconductor layers, each of which has substantially the same thickness and is made of a first nitride semiconductor containing aluminum, and a plurality of organic layers, each of which has substantially the same thickness and is made of organic material, are alternately laminated.
According to embodiments of invention, there is further provided a method for manufacturing an optical device comprising a reflector for reflecting light, said reflector is formed by comprising:
forming a laminated layers in which a plurality of semiconductor layers, each of which is made of a first nitride semiconductor containing aluminum, and a plurality of etching layers, each of which is made of a second nitride semiconductor having a lower content of aluminum than said first nitride semiconductor, are alternately laminated; and
heating said laminated layers in an atmosphere containing hydrogen to etch said plurality of etching layers exposed to the end face of said laminated layers to thereby form gaps between neighboring ones of said semiconductor layers.
According to embodiments of invention, there is further provided a method for manufacturing a method for manufacturing an optical device comprising a reflector for reflecting light, said reflector is formed by comprising:
forming a laminated layers in which a plurality of semiconductor layers, each of which is made of a first nitride semiconductor containing aluminum, and a plurality of etching layers, each of which is made of a second nitride semiconductor having a lower content of aluminum than said first nitride, are alternately laminated;
heating said laminated layers in an atmosphere containing hydrogen to etch said plurality of etching layers exposed to the end face of said laminated layers to thereby form gaps between neighboring ones of semiconductor layers; and
forming organic layers in said gaps.
According to embodiments of invention, there is further provided a method for manufacturing a surface emitting type device in which a first reflector for reflecting light from an active layer of said surface emitting device and a second reflector for reflecting light from said active layer are disposed to sandwich said active layer, at least one of said first reflector and said second reflector is formed by comprising:
forming a laminated layers in which a plurality of semiconductor layers, each of which is made of a first nitride semiconductor containing aluminum, and a plurality of etching layers, each of which is made of a second nitride semiconductor having a lower content of aluminum than said first nitride semiconductor, are alternately laminated; and
heating said laminated layers in an atmosphere containing hydrogen to etch said plurality of etching layers exposed to the end face of said laminated layers to thereby form gaps between neighboring semiconductor layers.
According to embodiments of invention, there is further provided a method for manufacturing a surface emitting type device in which a first reflector for reflecting light from an active layer of said surface emitting device and a second reflector for reflecting light from said active layer are disposed to sandwich said active layer, at least one of said first reflector and said second reflector is formed by comprising:
forming a laminated layers in which a plurality of semiconductor layers, each of which is made of a first nitride semiconductor containing aluminum, and a plurality of etching layers, each of which is made of a second nitride semiconductor having a lower content of aluminum than said first nitride semiconductor, are alternately laminated;
heating said laminated layers in an atmosphere containing hydrogen to etch said plurality of etching layers exposed to the end face of said laminated layers to thereby form a gap between neighboring said semiconductor layers; and
forming organic layers in said gaps.
Here, in the present specification, the nitrogen semiconductor includes the semiconductors of all compositions in which the composition ratios of x, y, z are varied in the respective ranges in a chemical formula of B1-x-y-zInx AlyGazN (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61, 0xe2x89xa6x+y+zxe2x89xa61), for example, also In0.4Ga0.6N, which is obtained when x=0.4, y=0, z=0.6 in the above chemical formula, and further includes a semiconductor in which a part of nitrogen, which is a V group element, is replaced by As (arsenic) or P (phosphorus). Here, anyone of the above three elements (In, Al, Ga) is contained as a III group element, and N (nitrogen) is surely contained as a V group element.